Fuse lead for electric lamps



Jan. 17, 1950 J. A. M. VAN LIEMPT 2,494,

FUSE LEAD FOR ELECTRIC LAMPS 7 Filed Dec. 4, 1946 Johannes Ani'o nius Maria Van Liemp b,

q in series with the filament Patented Jan. 17, 1950 FUSE LEAD FOR ELECTRIC LAMPS Johannes Antonius Maria van Liempt, Eindhoven,

Netherlands,

assignor to General Electric Company, Schenectady, N. Y.

Application December 4, 1946, Serial No. 714,078 In the Netherlands October 6, 1942 Section 1, Public Law 690, August 8,194.6 Patent expires October 6, 1962 There are already known electric incandescent lamps whereina fusible safety device is arranged present in these lamps. Such devices are utilized more particularly in lamps comprising a doubly or multiply coiled filament. The operation of such a device is based upon that which follows: During operation or when the filament burns out there may be produced within the lamp an are which may jumpacross the electrodes of the lamp and which brings about a short-circuit within the latter, so that there exists the possibility that the house service fuse connected in series with the lamp concerned blows or, if this fuse is not present or is dimensioned for an excessively high current capacity, that the lamp bursts asunder. In order to remove this drawback a safety device has been customarily provided within the lamp itself, which device, in the usually employed lamp constructions comprises, one fuse, preferably, however, two fuses, which are so dimensioned that they can sustain the operating current of the lamp during a sufficiently long period of time but, on th other hand, have a fusing time, which in the case of a short-circuit within the lamp, is several times as short as the fusing time of the house service fuse connected in series with the lamp. The lamp fuse is ordinarily provided in one or in both current supply wires in the stem tube of the lamp. Two forms of such fusible safety devices have found particular acceptance in practice. Firstly, use is frequently made of a construction which comprises two bare fuse wires combined with a cap insulated on the inside; there also is frequently employed another construction which comprises two fuse wires each of which is sealed into a closed glass tube. The first construction has the advantage of being cheap but the insulating layer on the inside of the cap has in this case to come up to high requirements. The second construction is perfectly reliable in service but is comparatively expensive.

In both cases it has been found that the safety device present in the lamp must comprise two fuses. In the first example mentioned hereinbefore this is necessary since otherwise an arc might still be produced between the end of the fuse secured to the cap and the second current supply wire which is not constructed as a fuse in this case. In the second case a construction with two fuses is necessary because with the use of only one fuse an arc might still be produced in the tube surrounding this fuse, which are entertains the short-circuit current. If, on the contrary, the lamp is constructed-so as to comprise 4 Claims. (01. 200-) two fuses, the voltage for each tube acquires, in the case of a breakdown within the lamp, so low a value that the production of an arc in one tube is completely excluded.

According to the invention, a single fuse in series with the filament is now, however, sufficient in an incandescent lamp wherein the fuse is constructed in accordance with the invention.

The lamp according to the invention is characterized by the feature that the fusible safety device provided in the lamp comprises a single fuse" of metal wire which is housed in a closed tube of insulating material which closely surrounds the fuse, said fuse being in intimate contact, at least over-part of its surface, with a certain quantity of a material which, due to the production of vapour, has an extinguishing effect on the arc.

The presence of the arc-extinguishing substance results in that when the filament burns out and when, as the case may be, subsequently thereto an arc is formed within the lamp, the temperature of the fuse present within the tube acquires so high a value that the arc-extinguishmg material vaporizes and develops a vapour pressure of so high a value that the arc which might be formed within the tube when the fuse wire burns out, is extinguished thereby. In this case it is essential that the tube in which the fuse is housed should closely surround the latter since otherwise there would be a chance that the developed vapour of the arc-extinguishing material would not have a pressure sufficient to extinguish the are produced.

It should benoted that it has already been pro posed to fill up the whole of the stem tube in which the two current supply wires are housed, with sand, magnesia and similar different substances. This construction is, however, completely unsuitable inter alia for wholesale manufacture.

It has been found that molybdenum oxide and zinc sulphide are particularly suitable for use as arc-extinguishing substances, for these substances have a vapour pressure which is not so high that they are vaporized when the glass tube is being sealed around the fuse wire and besides. they are neither decomposed under dissociation, which might lead to the result that when the fuse blows they might cause an excessively high vapour pressurewithin the tube, due to which the latter might burst and the metal vapour present in the fuse might reach the stem tube unhindered. Moreover, the vapour of these substances is sufliciently stable and does not dissociate so as to form ions which, instead of extinguishing the arc, might favor the latter.

The said substances have to be provided on the fuse with the aid of some binding agent or other. According to the invention, use is preferably made of a binder which itself is indifferent and which upon decomposition does not develop permanent vapours because otherwise they might give rise to the production of an excessively high pressure within the tube. According to one advantageous embodiment of the invention, ethyl silicate in an alcoholic solution is employed as the binder. When slightly heated, this substance is decomposed and evolves silicic acid which acts as an indifferent binder.

The invention will be explained more fully with reference to the accompanying drawing in which Fig. 1 is an elevation, partly in section, of an electric incandescent lamp comprising my invention; Fig. 2 is a diagrammatic illustration of the fused lead-in wire of the lamp; and Fig. 3 is a 'view of a modified form of fuse according to the invention.

Referring to Fig. 1, the lamp there shown comprises a glass bulb l to. which a cap 2 is attached. Within the bulb I is a stem which comprises a stem tube 3 and a pinch 4 in which the lead-in Wires or conductors 5, 9 of the lamp are provided. The lead-in wire 5 consists of a portion 6 of copper wire, a portion 1 formed by copper-coated wire and a portion 8 of nickel wire. In addition to a portion I of copper wire which extends from A to B, to a portion ll of sheath-wire which extends from C to D and to a portion I2 of nickel wire, the conductor 9 also comprises a fuse I3 of constantan wire of a thickness of 150 microns and coated with arc-extinguishing material, which extends from B to C and which is housed in a hermetically closed glass tube M which is sealed at E and at F to the portions of the copper wire 10 and the sheath wire I l which are present at these points, a slight clearance being present, as may be seen from Fig. 1, between the outside of the constantan wire [3 coated with arc-extinguishing material and the inside of the glass tube II. A doubly coiled filament I is mounted on the conductors 5 and 9. An exhaust tube 16 is provided in the usual manner in the stem tube 3.

The fuse wire 13 is coated in the present instance with zinc sulphide which, in the case of breakdown or when the filament I 5 burns out and in the event of the formation of an are between the conductors 5 and 9 due to the high temperature acquired by the fuse wire I3, is decomposed and on this account has an extinguishing effect on the are which may be produced when the wire [3 burns out. The glass tube 14 at such time remains intact and the danger of further damage such as the breakdown of the house service fuse is consequently eliminated.

For applying the zinc sulphide to the fuse wire 13 one may proceed as follows. For this purpose a bundle of lamp leading-in wires 9 of which only one is diagrammatically shown in Fig. 2 and which consist of the portions mentioned with reference to Fig. 1, is immersed for the portion A-C in a. suspension of zinc sulphide in ethyl silicate and immediately thereupon for the portion AB in ammonia, owing to which the suspension present on the portion AB is removed. Subsequently, this bundle is dried in a current of hot air, during which operation a layer of zinc sulphide remains on the portion 3-0, which layer consequently acts as the arc extinguishing material during the operation of the lamp in which such a fuse is mounted. Then a glass tube is hermetically sealed around the portion B-C as indicated in Fig. 1.

According to the invention, the fuse may also be constituted by a coiled wire as shown in Fig. 3. This affords the advantage that the arc-extinguishing substance gets better affixed between the turns of the fuse than on a straight wire. When use is made of such a fuse it is possible to provide thereon the arc-extinguishing material according to the so-called roll-gettering method, i. e. these fuses are rolled in a suspension of zinc sulphide in ethyl silicate, thus absorbing this suspension. Then, the fuses are removed from the suspension and dried and the excessive quantity of suspension which, as the case may be, is present on the outside of the fuses may be removed with the aid of a brush or a pencil. In this case, the arc-extinguishing material is consequently present chiefly on the inside of the wound fuse and only part of the wire surface is therefore in intimate contact with the arc-extinguishing material.

The fuse according to the invention may be utilized, of course, in incandescent lamps of any type and therefore, for example, in flashlight lamps.

What I claim is:

1. A fuse structure comprising an elongated conductor having a portion of its length constituted by a fuse element, a tube of vitreous material closely surrounding said fuse element and fusion-sealed at its ends to said conductor to hermetically seal the fuse element within said tube, and a coating on said fuse element of a material which will not decompose under dissociation and which vaporizes at a temperature above the fusion temperature of said tube but below the melting point of said fuse element and the vapor of which possesses arc-extinguishing properties, said material being selected from the group consisting of zinc sulphide and molybdenum oxide.

2. A fuse structure as set forth in claim 1 wherein the arc-extinguishing material coated on the fuse element consists of zinc sulphide.

3. A fuse structure as set forth in claim 1 wherein the arc-extinguishing material coated on the fuse element consists of molybdenum oxide.

4. A fuse structure as set forth in claim 1 wherein the fuse element consists of a coiled metal wire coated with said vaporizable material.

J OHA-NNES ANTONIUS MARIA VAN LIEMPT.

REFERENCES CITED The following'references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,288,724 Snelling Dec. 24, 1918 1,819,198 Reichmann et al. Aug. 18, 1931 1,821,214 Gustin Sept. 1, 1931 2,021,758 Van Horn Nov. 19, 1935 2,145,105 Aisch Jan. 24, 1939 2,147,584 Thomas Feb. 14, 1939 2,179,455 Spaeth Nov. 7, 1939 2,183,952 Anderson Dec. 19, 1939 FOREIGN PATENTS Number Country Date 16,500 Great Britain 1900 10,082 Great Britain Aug. 7, 1914 

